This invention relates to a process for producing microspherical pitch and green coke particles, and more specifically to a process for producing such microspherical pitch particles made of any of pitches from processes for treating petroleum, coal or the like, or from any of naturally occurring bitumens or asphalts, and which can be handled as easily as a fluid for convenience in transportation and storage.
Generally, pitch and raw or green coke are not readily distinguishable from each other from the compositional viewpoint. The same applies in this invention. The pitch and green coke spheres according to the invention overlap in their ranges of fixed carbon content and hydrogen-carbon ratio. Nevertheless, there are clear distinctions between the two in the manufacturing process (degrees of decomposition and polymerization) and in physical and chemical properties of the products. The two products are hereinafter referred to as pitch spheres and green coke spheres.
Pitches are available in abundance from the processes for treating and refining petroleum, coal and the like. For example, treatments of petroleum bottom (residual) oils, tar sands, and oil shales, and coal coking and liquefaction processes afford pitches. Besides, there occur bitumens and asphalts in nature. Part of these pitches is in use, after appropriate treatments, for varied applications, e.g., as electrode-, steel-, and other binder pitches, solid fuels such as electrode coke, carbonaceous and other coke fuels, and as feedstocks for fuel gas and hydrogen gas production.
However, as is well-known with the naturally occurring bitumens and asphalts, those pitches are either viscous liquids or solids which become viscous as the temperature rises. The inherent viscosities make them difficult to handle for transportation and storage, thus limiting their fully effective utilization.
The present invention provides novel, spherical pitch and green coke products which eliminate the disadvantages of the currently available products and permit easy handling like a fluid without adhesiveness. The pitch and green coke spheres, which are so easy to transport and store, are very helpful in settling the problems in processes for treating heavy distillates and bottoms to which increasing importance is being attached. Of the crude oils in production and on market, heavy ones are accounting for increasing percentages, while another general tendency is a gradual shift in demand from heavy to light and lighter petroleum products. Consequently, there is an urgent need for expanding the capacities of processes for converting and upgrading heavy or bottom oils to lighter materials. Additionally early development of substitute energies for petroleum is being called for. Attempts to recover oils from tar sands and oil shales and development of new coal liquefaction processes are also under way. Heavy distillates or oils from these sources are to be fed, too, to the heavy-to-light conversion and upgrading processes. Those processes naturally give carbonaceous residues, which present a number of handling and application problems yet to be solved with the existing installations for the heavy oil treating processes.
This will be explained, by way of example, in connection with typical processes for treating petroleum bottom oils, namely, delayed coking, Eureka process, Fluid Coking, and Flexicoking processes. Delayed coking, which is a semibatch process, produces residual green coke in coke drums which must be crushed and taken out at regular intervals by hydraulic or mechanical means. The crushed mass is difficult to discharge, and the product coke is inconvenient to transport and store because of its moisture and other contents. The product also involves difficulties in use as fuel. The Eureka process, again for semibatch operation, yields residual pitch in a liquid form, which can be continuously taken out and cooled solid by a flaker for use as binder for iron and steel. Although the residue the process gives is a pitch easy to take out, it still entails some inconvenience in transportation and storage. Moreover, in the present state of the art, there is a quantitative limit to the application of the pitch as the binder or the like. Fluid Coking gives coarse coke pieces as the residue, but because relatively high temperatures are used in processing, the coke has rather poor combustibility and hence its value as fuel is low. Flexicoking further gasifies the residual coke pieces obtained above. The gasified product is convenient for transportation but not for storage. In addition, the gas is low in calorific value and is limited in use as fuel.
The present inventors conceived the idea of continuously taking out of the system, in the form of pitch, the carbonaceous residue that results from a process of treating heavy residual bottoms, and then forming the pitch into microspherical pitch or green coke particles that can be handled like a fluid, in the belief that the product would then be convenient for transportation and storage, usable directly as fuel in many cases, and be efficiently gasifiable when necessary, thus contributing greatly to the utilization of the carbonaceous residues from the bottom treating processes that leave many problems yet to be solved. Intensive investigations based on the concept have now led to the provision of a process for producing pitch and green coke spheres capable of solving the problems pertaining to the bottom oil treating process.